<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      var a = 100
      function f() {
        return this.a
      }
      console.log(f()) //100
      let o = { a: 200 }

      let g = f.bind(o)
      console.log(g()) //200
    </script>
  </body>
</html>
